In a heterogeneous network deployed with small cells, the dual connectivity (DC) technology can be used to increase the throughput of a User Equipment (UE), enhance the mobility robustness, decrease the network signaling overhead, etc.
FIG. 1 is a schematic diagram of making dual connectivity in the relevant art. As illustrated in FIG. 1, a base station (such as an eNB) can configure dual connectivity for a UE in a connected status and having a multi-transceiving function with. When dual connectivity is configured, schedulers on two different eNBs (eNodeBs) are employed to provide radio resources to the UE for data transmission, and the two eNBs are usually connected to each other through a non-ideal backhaul X2 interface.
In which, an eNB retaining an S1-MME interface with a Mobility Management Entity (MME) is referred to as Master eNB (MeNB), and service cells associated with the MeNB constitute a Master Cell Group (MCG); the other eNB, which is only used to provide additional radio resources, is referred to as Secondary eNB (SeNB), and correspondingly, service cells associated with the SeNB constitute a Secondary Cell Group (SCG).
In the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), a bearer refers to a data transmission channel and a configuration thereof, and different bearers may have different configurations to transmit services required by different Qualities of Service (QoS). The bearer on the radio interface is referred to as Radio Bearer (RB), for example a user plane bearer is referred to as Data Radio Bearer (DRB), and a control plane bearer is referred to as Signaling Radio Bearer (SRB). When dual connectivity is configured, the RBs can be classified into three types: MCG bearer, SCG bearer and split bearer.
FIG. 2 is a schematic diagram of a radio protocol stack corresponding to a bearer under dual connectivity. As illustrated in FIG. 2, in the perspective of protocol stack, the MCG bearer refers to a bearer which performs corresponding data transmission only using MeNB resources and to which a radio protocol stack corresponding is only located on the MeNB, the SCG bearer refers to a bearer which performs corresponding data transmission only using SeNB resources and to which a radio protocol stack corresponding is only located on the SeNB, and the split bearer refers to a bearer which uses both MeNB resources and SeNB resources and to which a radio protocol stack corresponding is on both of the MeNB and the SeNB.
As to the UE configured with dual connectivity, the network side can determine the type of the bearer for which the service of the UE is configured according to the network load and the service attribute of the UE, i.e., whether the service of the UE is configured to be transmitted on the MCG bearer, or the SCG bearer, or the split bearer.
On the other hand, in the relevant art, the network supports the addition, modification and release of the DRB through a procedure (RRCConnectionReconfiguration) of radio resource management connection reconfiguration. The configuration (including reconfiguration) of the DRB and the configuration limitation are described as follows:                Evolved Packet System (EPS) bearer identity (eps-Bearerldentity). This parameter is only configured when the DRB is established, and cannot be configured under other condition.        DRB identity (drb-Identity). This parameter remains unchanged during the presence of the DRB.        Packet Data Convergence Protocol (PDCP) configuration (pdcp-Config). This parameter must be configured when the DRB is established, selectively configured in a case of handover and RRC reestablishment, and cannot be configured under other condition.        Radio Link Control (RLC) configuration (rlc-Config). This parameter must be configured when a DRB is established, and selectively configured under other condition.        Logical channel identity (logicalChannelldentity). This parameter is only configured when the DRB is established, and cannot be configured under other condition.        Logical channel configuration (logicalChannelConfig). This parameter must be configured when the DRB is established, and selectively configured under other condition.        
Generally, the network side takes the DRB identity as an anchor for the DRB management, including the establishment, modification and release of the RB. In a case where the service site of the UE is changed (e.g., handed over), if the target site and the source site have different versions, it is possible that the target site cannot parse the configuration of the eNB by the source site. At that time, the target site will adopt a full configuration, and the network side takes the EPS bearer identity as an anchor for the RB management, including the establishment and release of the RB.
In addition, when dual connectivity is configured, the MeNB and the SeNB independently maintain the configuration of the logical channel, including independently configuring the logical channel identity. That is, the MeNB and the SeNB can configure different RBs of the UE with the same or different logical channel identities.
For example, in FIG. 2, the logical channel identities corresponding to bearer 1 and bearer 3 are independently configured by the MeNB and the SeNB, respectively, and they may be the same as or different from each other. Similarly, the DRB identity under the scene of dual connectivity may also be independently configured by the MeNB and the SeNB, i.e., the MeNB and the SeNB can configure different RBs of the UE with the same or different DRB identities.
It shall be noted that the above description of the background is merely provided for clear and complete explanation of the present disclosure and for easy understanding by those skilled in the art. And it shall not be understood that the above technical solution is known to those skilled in the art as it is described in the background of the present disclosure.